There is a folder that appears to be quite big when you analyze your drive: Windows\WinSxS. It reports many gigabytes of files. If you are low on space, you might be tempted to delete it. The problem is that the folder is full of hard links to files that are already stored in other places. In order to determine the true size of the folder, run this command with elevated privileges:

Deleting the folder or the files inside it will break your machine. Moving the files and copying them back will delete the hard links (freeing no space) then copy actual files instead, wreaking havoc with your system.